In order to remove particulates, organic matter, metals, etc. from the surfaces of electronic materials such as silicon substrates for semiconductors, glass substrates for liquid crystals, quartz substrates for photomasks, etc., functional cleaning water prepared by dissolving a specific gas in ultrapure water by a gas dissolving device, and then further adding trace amounts of chemicals as necessary has come to be used in place of high concentration chemical solutions. As the specific gas used in the functional cleaning water, in addition to carbon dioxide gas, hydrogen gas, oxygen gas, ozone gas, there are also inert gases, etc. such as noble gases. Various methods of dissolving carbon dioxide gas and hydrogen gas are being considered.
In particular, carbonated water is being used in order to rinse a cleaned object surface without electrically charging the cleaned object or nozzle. In other words, when using ultrapure water in cleaning, due to the magnitude of the insulation property thereof, the cleaned object may be electrically charged due to the friction with the cleaner and, for example, such as in a case of there being a fine circuit pattern on the cleaned object, the circuit thereof may be damaged from this electric charge. Carbonated water with enhanced conductivity by dissolving carbon dioxide gas in ultrapure water is being used in order to prevent this.
As a production method of carbonated water, a technique of degassing dissolved gas in ultrapure water using a gas-permeable membrane module of gas-permeable hollow fiber membranes, and subsequently dissolving a predetermined gas using the gas-permeable membrane module is often being used.
As the gas-permeable hollow fiber membrane, a membrane prepared using linear low-density polyethylene as the raw material of the homogeneous layer is exemplified in Patent Document 1.
A gas-permeable hollow fiber membrane consisting of TPX (polymethylpentene, PMP) having a non-porous outer surface is exemplified in Patent Document 2.
In a gas separation application, when water vapor is contained in the gas that is the separation target thereof, the water vapor having permeated from the target liquid of degassing may condense at the porous support layer on the surface of the membrane to decrease the gas permeability, and thus periodic drainage of drain water or drying of the gas-permeable membrane by way of high-temperature gas has been required (Patent Document 5).
It has been demanded to balance conflicting abilities like moderate hydrophobicity for realizing affinity between mixed gas and the membrane surface, while on the other hand, hydrophilicity for the separation performance with relation to water vapor not to decline over time.
For example, as a non-porous gas separation membrane with high hydropholicity to water, an ethylene-vinyl alcohol-based polymer composite membrane for gas separation consisting of an ethylene-vinyl alcohol-based polymer and amine compound (Patent Document 3) has been exemplified.
In addition, as a method for realizing hydrophilicity at the membrane surface, a hydrophilization technique by way of surfactants has been exemplified (Patent Document 4).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. H11-47565
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2010-155207
Patent Document 3: Japanese Examined Patent Application Publication No. H06-96102
Patent Document 4: Japanese Unexamined Patent Application, Publication No. S63-277251
Patent Document 5: Japanese Unexamined Patent Application, Publication No. 2009-219997